Monocrystalline diamond detector for online monitoring during synchrotron microbeam radiotherapy

At a Glance

Metadata	Details
Publication Date	2023-10-10
Journal	Journal of Synchrotron Radiation
Authors	Francesca di Franco, Nicolas Rosuel, L. Gallin-Martel, M.-L. Gallin-Martel, Mostafa Ghafooryan-Sangchooli
Institutions	Centre National de la Recherche Scientifique, Institut polytechnique de Grenoble
Citations	11
Analysis	Full AI Review Included

Technical Documentation & Analysis: MPCVD Diamond for Synchrotron Dosimetry

Executive Summary

This documentation analyzes the research demonstrating the feasibility of using Monocrystalline Chemical Vapor Deposition (MPCVD) diamond detectors for online monitoring during Synchrotron Microbeam Radiation Therapy (MRT).

Core Achievement: Successful development and characterization of a striped Monocrystalline Diamond (SCD) portal detector prototype for real-time, high-spatial-resolution dosimetry in ultra-high flux MRT environments.
Performance Validation: The detector exhibited a highly linear response across four orders of magnitude, confirming suitability for dose rates up to 1.2 x 10⁴ Gy s⁻¹, exceeding nominal clinical MRT rates.
Material Excellence: The SCD material demonstrated near 100% Charge Collection Efficiency (CCE) and excellent radiation hardness, confirming diamond’s superiority over silicon and other conventional dosimeters in high-flux, low-energy photon fields.
Spatial Resolution: The striped geometry (60 µm interstrip spacing) successfully resolved alternating microbeam peaks and interbeam valley doses, crucial for spatially fractionated dosimetry.
Optimization Insight: Monte Carlo simulations determined that a 150 µm SCD thickness is optimal for minimizing background noise in the interbeam (valley) areas, guiding future detector design.
Future Scaling: The research paves the way for a full-scale, 153-strip, 30 mm wide SCD detector, requiring large-area, high-purity MPCVD diamond substrates and advanced metalization patterning.

Technical Specifications

The following table summarizes the critical performance metrics and material specifications extracted from the research paper.

Parameter	Value	Unit	Context
Diamond Material Type	Monocrystalline Diamond (SCD)	N/A	MPCVD grown
Detector Thickness (Prototype)	550	µm	Bulk SCD used for initial tests
Optimal Thickness (Simulated)	150	µm	Minimizes interbeam background noise
Strip Width	178	µm	Electrode dimension
Interstrip Spacing	60	µm	Defines spatial resolution
Strip Height	3	mm	Active area dimension
Maximum Linear Dose Rate	1.2 x 10⁴	Gy s⁻¹	Confirmed linearity in water
Typical MRT Dose Rate	6 x 10³	Gy s⁻¹	Nominal clinical rate
Charge Collection Efficiency (CCE)	~100	%	Confirmed via spectroscopy tests
Operational Energy Range	50-500	keV	Synchrotron X-ray spectrum
Leakage Current (550 µm SCD)	0.8 ± 0.3	nA	Measured background level
Experimental Agreement (Phantom)	< 2	%	Difference between simulation and experiment
Metalization Layers Used	TiAl, Al	N/A	Electrode materials

Key Methodologies

The experimental success relied on precise material processing, custom electronics integration, and rigorous testing under synchrotron conditions.

Material Sourcing: High-purity Monocrystalline Diamond (SCD) wafers (550 µm and 150 µm thickness) were used as the base material, leveraging diamond’s intrinsic properties (high mobility, wide bandgap) for fast, radiation-hard detection.
Strip Detector Fabrication: An eight-strip geometry was defined on the SCD surface. This involved depositing a thin layer of Aluminum (Al) or TiAl for the front-side strip electrodes and fully metalizing the back side for bias application.
Electronic Integration: The striped detector was coupled with a custom eight-channel ASIC circuit designed for high-speed charge integration and digitization (using a Charge-to-Digital Converter, QDC) with integration times as low as 1 ms.
Synchrotron Irradiation: Tests were conducted at the European Synchrotron Radiation Facility (ESRF) ID17 biomedical beamline, utilizing both the MRT hutch (polychromatic, high flux) and the monochromatic hutch (energy characterization).
Dosimetry Characterization: The detector response was measured as a function of dose rate (tuned using PMMA absorbers) and photon energy (33-130 keV monochromatic X-rays).
Spatial Mapping: Horizontal scans were performed using a 25 µm step microbeam to map the response of individual strips and confirm the ability to resolve the 60 µm interbeam valley regions.
Clinical Validation: The prototype was tested using both homogeneous (RW3 water equivalent) and realistic anthropomorphic head phantoms, with results benchmarked against Monte Carlo simulations (GATE).

6CCVD Solutions & Capabilities

The development of advanced diamond detectors for MRT requires materials and processing capabilities that align perfectly with 6CCVD’s core expertise in MPCVD diamond engineering. 6CCVD is uniquely positioned to supply the materials and customization required to replicate, scale, and advance this critical research.

Applicable Materials

To achieve the required 100% CCE and high-speed response demonstrated in this paper, the highest quality SCD is essential.

Optical Grade SCD Wafers: 6CCVD provides high-purity, low-nitrogen Monocrystalline Diamond (SCD) necessary for maximizing charge carrier mobility and minimizing deep traps, ensuring stable, linear response at ultra-high dose rates.
Precision Thickness Control: The research identified 150 µm SCD as the optimal thickness for minimizing interbeam background noise. 6CCVD specializes in growing and polishing SCD wafers to precise thicknesses, ranging from 0.1 µm up to 500 µm, allowing researchers to implement the optimal design derived from their Monte Carlo simulations.

Customization Potential

The transition from the 8-strip prototype to the planned 153-strip, 30 mm wide detector requires advanced patterning and large-area capabilities.

Requirement from Research Paper	6CCVD Solution & Capability	Technical Advantage
Custom Dimensions (30 mm wide array)	Custom SCD/PCD Plates: We provide SCD substrates cut to custom dimensions (e.g., 4.5 mm x 4.5 mm chips or larger arrays). We offer PCD plates up to 125 mm for large-scale, cost-effective arrays.	Supports the scaling of the detector from prototype to the full 153-strip clinical device.
Micrometric Strip Patterning	Precision Laser Cutting & Lithography: In-house services for defining micrometric features (e.g., 178 µm strips, 60 µm spacing) with high accuracy (Ra < 1nm polishing for SCD).	Ensures the high spatial resolution required to differentiate peak and valley doses in MRT.
Electrode Metalization (TiAl, Al)	Comprehensive In-House Metalization: We offer deposition of standard and custom electrode stacks, including Ti, Pt, Au, Pd, W, Cu, and can replicate the TiAl or Al layers used in this study.	Facilitates optimization of ohmic and Schottky contacts for high-speed charge readout and long-term stability under high radiation flux.
Global Logistics	Global Shipping (DDU/DDP): Reliable, insured global delivery of sensitive diamond materials.	Ensures rapid and secure delivery of custom-engineered diamond components to synchrotron facilities worldwide (e.g., ESRF).

Engineering Support

The successful implementation of this detector relies on optimizing the diamond material properties (e.g., trap density, surface quality) to eliminate transient effects (priming/overshoot) observed under X-ray tube irradiation. 6CCVD’s in-house PhD team specializes in defect engineering and surface termination, offering consultation to assist researchers in selecting the ideal SCD grade and processing recipe for similar Synchrotron Dosimetry or FLASH Radiotherapy projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

Microbeam radiation therapy (MRT) is a radiotherapy technique combining spatial fractionation of the dose distribution on a micrometric scale, X-rays in the 50-500 keV range and dose rates up to 16 × 10 3 Gy s −1 . Nowadays, in vivo dosimetry remains a challenge due to the ultra-high radiation fluxes involved and the need for high-spatial-resolution detectors. The aim here was to develop a striped diamond portal detector enabling online microbeam monitoring during synchrotron MRT treatments. The detector, a 550 µm bulk monocrystalline diamond, is an eight-strip device, of height 3 mm, width 178 µm and with 60 µm spaced strips, surrounded by a guard ring. An eight-channel ASIC circuit for charge integration and digitization has been designed and tested. Characterization tests were performed at the ID17 biomedical beamline of the European Synchrotron Radiation Facility (ESRF). The detector measured direct and attenuated microbeams as well as interbeam fluxes with a precision level of 1%. Tests on phantoms (RW3 and anthropomorphic head phantoms) were performed and compared with simulations. Synchrotron radiation measurements were performed on an RW3 phantom for strips facing a microbeam and for strips facing an interbeam area. A 2% difference between experiments and simulations was found. In more complex geometries, a preliminary study showed that the absolute differences between simulated and recorded transmitted beams were within 2%. Obtained results showed the feasibility of performing MRT portal monitoring using a microstriped diamond detector. Online dosimetric measurements are currently ongoing during clinical veterinary trials at ESRF, and the next 153-strip detector prototype, covering the entire irradiation field, is being finalized at our institution.

Tech Support

Original Source

DOI: https://doi.org/10.1107/s160057752300752x